1. Field of Invention
This invention relates to microelectromechanical system (MEMS) based structures and microelectromechanical system (MEMS) based systems including at least one bistable structure. This invention also relates to methods for fabricating such structures and systems, as well as methods for actuating microelectromechanical system based systems.
2. Description of Related Art
Bistable beams are known for use in microelectromechanical system (MEMS) based systems. Such bistable beams have applications in, for example, digital data storage and electrical and optical switching.
For example, a tunable micromechanical bistable system is described by M. T. A. Saif in “On a Tunable Bistable MEMS—Theory and Experiment”, Journal of Microelectromechanical Systems, Vol. 9, No. 2, pp. 157–170, June 2000. The bistable system consists of a long slender micromechanical beam attached to an actuator. The beam is subjected to a transverse force at the middle and a residual stress developed during fabrication. The actuator generates a compressive force along the axial direction of the beam so that the beam buckles along the transverse direction into one of two equilibrium states.
Another example of a known beam structure is described by Vangbo et al. in “A Lateral Symmetrically Bistable Buckled Beam”, J. Micromech. Microeng., 8 (1998), pp. 29–32. As described, a lateral symmetrically bistable beam is snapped into the structure of a microelectromechanical system (MEMS) based device and held in a fixed position by spring forces. The beam structure consists of a released upright beam that has been oxidized to induce tensile stress or has a compressive film deposited thereon.
U.S. Pat. No. 6,168,395 to Quenzer et al. describes a bistable electrostatic actuator with pneumatic or liquid coupling. The bistable actuator has buckled membrane sections that are driven by enclosed electrodes. The membranes operate in counteraction, such that pulling one membrane down pushes the other membrane up. The bistable actuator is particularly designed for a microvalve application and uses curved-shaped electrodes.
U.S. Pat. No. 6,303,885 to Hichwa et al. describes a bistable micro-machined electromechanical switch. The bistable switch includes a switch element that is suspended between portions of a switch body by a plurality of spring arms that are attached at walls of hollow body portions of a center beam. The spring arms and hollow beam walls deform in response to a motive force of an actuator to move between the stable states.